1. Technical Field
The present invention relates to a piezoelectric actuator, a liquid ejection head, and a liquid ejection apparatus.
2. Related Art
For example, a liquid ejection head which ejects liquid droplets of ink or the like has been known in a liquid ejection apparatus such as an ink jet printer. The liquid ejection head includes a piezoelectric actuator for changing pressures in pressure generation chambers. The piezoelectric actuator has a piezoelectric layer which is sandwiched between an upper electrode and a lower electrode. If the piezoelectric layer is deformed by a driving signal or the like, a vibration plate can be bent. With this, the liquid ejection head can eject ink or the like supplied into the pressure generation chambers through nozzle holes.
The piezoelectric layer of such piezoelectric actuator has a driving region which is sandwiched between the upper electrode and the lower electrode, and non-driving regions which are not sandwiched between the upper electrode and the lower electrode (see, International Publication WO 2005/028207). Since an electric field is applied to an inner side of the driving region by a driving signal or the like, the piezoelectric layer is actively deformed. However, since an electric field is hardly applied to the non-driving regions at the outside of the driving region, the piezoelectric layer cannot be actively deformed. Therefore, a stress such as distortion is concentrated in the vicinity of boundaries between the driving region and the non-driving regions. This arises a possibility that cracking is generated on the piezoelectric layer.
In consideration of the above problem, a piezoelectric actuator on which cracking is difficult to be generated in the vicinity of the boundaries between the driving region and the non-driving regions and which has improved reliability, or the like, has been desired.